Underground utility locating is the process of identifying and marking the buried pipes and cables on a property before anyone digs. You start it by calling 811, the national one-call number. The call center notifies every utility company with infrastructure near your dig site, and each company sends a locator who marks the approximate horizontal path of their lines on the ground using color-coded paint or flags. Federal law requires anyone planning excavation to use their state’s one-call system before breaking ground.1Federal Communications Commission. FCC Designates 811 as Nationwide Number to Protect Pipelines and Utilities The U.S. Department of Transportation reports that calling 811 before digging gives you a 99 percent chance of avoiding an incident.2U.S. Department of Transportation. Call 811 Before You Dig
When You Have to Call
Federal pipeline safety law requires anyone planning demolition, excavation, tunneling, or construction to contact the appropriate one-call notification system before starting work.3Office of the Law Revision Counsel. 49 USC 60114 – One-Call Notification Systems Every state has adopted a one-call system to comply, and most states extend the requirement beyond pipelines to cover water, sewer, electric, and telecom lines as well.
The rule applies to projects of all sizes. Installing a fence, planting a tree, building a deck, or setting a mailbox post all count as excavation in most jurisdictions. Some states carve out narrow exemptions for shallow gardening, routine agricultural tilling, or normal road grading, and the exemptions often come with depth limits. The safe assumption is that any project involving a shovel, auger, or machine breaking the surface requires a locate request. Emergency excavations, like repairing a burst water main, are widely exempt from the advance-notice requirement, though you still need to notify the one-call center as soon as practical.
How to Request a Locate
Before you call, gather the property’s exact street address, the nearest cross streets, a description of where on the property you plan to dig, the type of work, and the maximum depth you expect to reach. Depth matters because it tells utility companies whether their deeper infrastructure is at risk.
Dialing 811 from any phone connects you to the regional one-call center for your area. A representative collects your site information and notifies every utility company with buried infrastructure near your dig location. Most regions also offer online portals where you can submit the same information through a digital map interface, which is useful for contractors managing multiple sites.
The American Public Works Association recommends marking the boundaries of your planned dig area with white paint or white flags before the locator arrives.4American Public Works Association. APWA Guide – Uniform Temporary Marking of Underground Facilities This pre-marking keeps the locator focused on the area that matters and prevents paint across the rest of your yard. White is the designated color for proposed excavation, so it won’t be confused with any utility marking.
Once the request is processed, the system issues a ticket number. Keep it for the entire project. It’s your proof that you followed the law, and you’ll need it to check on markings, request a re-mark, or defend yourself after a strike.
What 811 Covers and What It Doesn’t
This is where most homeowners get caught off guard. The 811 system only locates utility-owned infrastructure, and that ownership typically ends at the meter or the property line. Anything on your side of the meter belongs to you, and no one dispatched by 811 will mark it.
Private lines that 811 will not locate include:
- Water and sewer service lines running from the meter or sewer main to your house
- Gas piping beyond the gas meter, including lines to outdoor grills or fire pits
- Electric wiring from the meter to a detached garage, workshop, pool equipment, or landscape lighting
- Sprinkler and irrigation lines, propane lines from a tank, septic system piping, and underground pet fences
If your excavation could cross any of these, you need to hire a private utility locator separately. These services typically charge by the hour or by the project, with costs varying based on property size and complexity. A ruptured private gas line is just as dangerous as hitting a public main.
What Happens When the Locator Arrives
Each utility company sends a locator, or a contracted locating firm, to identify and mark their buried lines. The job is to trace the horizontal path of underground infrastructure and mark the surface above it. Most locators use two complementary technologies depending on what’s buried.
Electromagnetic Locating
For metallic pipes and cables, a transmitter connects to a known access point such as a meter, valve, or tracer wire and sends a signal along the conductive line. The technician walks the surface with a handheld receiver that detects the signal and follows its peaks to trace the route. The method works for metal water pipes, gas lines, and energized electrical cables. The Federal Highway Administration notes that electromagnetic equipment cannot detect fiber optic, concrete, or PVC pipes on its own, though many utilities install metallic tracer wires alongside non-metallic lines specifically so they can be located later.5Federal Highway Administration. Underground Utilities – Magnetic Locators
Ground Penetrating Radar
For non-metallic pipes without tracer wires, locators turn to ground penetrating radar. The equipment sends radio waves into the soil and reads the reflections that bounce back when the signal hits something with a different density than the surrounding earth. GPR works well in dry, sandy, or loamy soils but struggles in clay-heavy or waterlogged ground, where the signal attenuates before reaching the utility. Rocky terrain, thick vegetation, surface clutter, and reinforced concrete also reduce effectiveness. The deeper a line sits, the more these factors compound, so GPR is most reliable for utilities within the first few feet of the surface.
What the Marks Tell You
Marks show only the horizontal position of a buried line. They do not show depth. Utility companies are generally reluctant to estimate depth because the original installation depth can shift over time due to erosion, grading, or frost heave. Never assume a line sits at any particular depth just because it was installed at a standard depth years ago.
Reading the Colors and Symbols
Painted lines and flags follow the APWA Uniform Color Code, which assigns a specific color to each type of buried utility:6American Public Works Association. Uniform Color Code
- Red: electric power lines, cables, and lighting cables
- Yellow: gas, oil, steam, and other hazardous materials
- Orange: telecommunications, cable TV, alarm, and signal lines
- Blue: potable water
- Green: sewers and drain lines
- Purple: reclaimed water, irrigation, and slurry lines
- White: proposed excavation boundaries (your pre-marks)
- Pink: temporary survey markings
Locators also paint letters alongside the colored lines to identify the utility or the pipe material. A “G” inside a yellow line indicates gas; a “W” in blue marks water. Straight painted lines trace the run of the utility, and arrows show direction changes or connection points. When the surface directly above a line is obstructed by a structure, pavement scheduled for removal, or a material pile, locators place offset markings on a clear area nearby with notations indicating the actual line is a specific distance away.4American Public Works Association. APWA Guide – Uniform Temporary Marking of Underground Facilities
The Waiting Period and Tolerance Zone
After your ticket is filed, the law gives utility companies a set window to complete their markings before you can dig. Most states require a minimum of 48 hours of advance notice, calculated in working days that exclude weekends and holidays. Some states allow up to 72 hours. Digging before this window closes is a violation in every state, regardless of whether any damage results.
Once marks appear, every line has a tolerance zone extending outward from them, typically 18 to 24 inches on each side depending on your state. Inside that buffer you cannot use mechanical equipment like backhoes, excavators, or augers. Marks represent approximate locations, and a utility might sit slightly outside the painted line. Heavy equipment can shear through a gas line that’s only inches off.
Hand Digging and Vacuum Excavation
Inside the tolerance zone, the traditional requirement is hand digging with shovels. Many states and utility operators now also accept vacuum excavation, sometimes called “soft dig.” The method uses a blast of pressurized air or water to loosen soil, then a vacuum hose removes the debris. It reduces the risk of a shovel blade striking a line, keeps workers on the surface away from trench collapse hazards, and can handle frozen ground when hot water is used. Not every jurisdiction treats vacuum excavation identically to hand digging, so check your state’s rules before relying on it exclusively.
Ticket Expiration
Locate tickets don’t last forever. Depending on your state, a ticket remains valid for roughly 10 to 30 working days. If your project runs longer, or if the paint and flags become illegible due to weather or construction traffic, submit a renewal or re-mark request before continuing work. The renewal generates a new ticket number and restarts the validity clock. Letting a ticket expire and continuing to dig is treated the same as never having called.
Confirming Every Utility Has Responded
Not every utility company responds at the same speed, and some may determine they have no facilities in your area. A growing number of states now require a “positive response” system where each notified utility must confirm either that they’ve completed their markings or that they have no conflict with your excavation. The confirmation might come as markings on site, a callback, or an update in an online portal. If any utility has not responded by the time your waiting period ends, do not assume the area is clear. Contact the one-call center to report the missing response before digging. Starting excavation when you know or suspect a utility hasn’t been marked exposes you to liability for any damage.
If You Hit a Line
Even with proper marking, strikes happen. The first few minutes determine whether the situation stays manageable or escalates.
If you hit a gas line and smell gas or hear hissing, stop all work and evacuate the area immediately. Do not use any electrical device near the leak, including your cell phone, because even a small spark can ignite natural gas. Move to a safe distance, then call 911 and the gas company’s emergency line from a location well away from the leak. Do not attempt to stop the flow of gas or operate pipeline valves. Never try to extinguish a fire fed by a gas line; trained pipeline personnel need to shut off the fuel source. Gas can migrate through sewer and storm drain lines over surprising distances, so nearby structures should be checked for accumulation.
For any utility strike, federal law requires you to promptly report the damage to the utility owner, and if the damage releases any flammable, toxic, or corrosive substance, to call 911.3Office of the Law Revision Counsel. 49 USC 60114 – One-Call Notification Systems Even strikes that seem minor, like nicking a water line or scraping cable insulation, should be reported. Unreported damage can worsen over time and create liability long after the project ends.
Penalties for Skipping the Process
At the federal level, anyone who knowingly excavates without using the one-call system and then damages a pipeline causing death, serious injury, or more than $50,000 in property damage faces up to five years in prison. Willfully destroying an interstate pipeline facility carries up to 20 years, and if someone dies, the sentence can extend to life.7Office of the Law Revision Counsel. 49 USC 60123 – Criminal Penalties Failing to report damage you know about triggers its own penalty under the same statute.
State penalties vary but generally include civil fines for failing to call 811, digging before the waiting period expires, or excavating inside the tolerance zone with prohibited equipment. Fines typically range from a few hundred dollars for a first offense up to tens of thousands for repeat violations or strikes that cause outages. Beyond fines, excavators who damage a utility are almost always liable for the cost of repairs, and that bill climbs quickly when a gas main rupture triggers emergency response, road closures, and service restoration for an entire neighborhood. Keep your ticket number, photograph the marks before you dig, and document your compliance at each step. If a dispute arises, that record is your defense.